1. Field of the Invention
This invention pertains to processing insulated conductors, and more particularly to apparatus for accurately controlling the strip lengths of insulated conductors.
2. Description of the Prior Art
The search for ever higher levels of production and uniformity in stripped insulated conductors has led the industry to investigate tooling components as a possible source of strip related failures. Tooling components include the spacers that have long been used to separate the cutoff and stripping blades of insulated conductor processing machines.
In FIG. 1, an insulated conductor 35 is shown composed of an inner conductor 39 covered with an insulation layer 41. A long length of insulated conductor 35 is severed into discrete pieces 36 along lines 43. The insulation 41 is shown stripped back from the line of severance 43 to the lines 45 and 47. The distances A1 and A2 between the severance line and the lines 45 and 47 are called the strip lengths. The strip lengths of the opposite ends of a cut insulated conductor piece 36 may, but need not, be equal. In some applications, the insulation on one of the ends of the cut pieces is not stripped.
Referring to FIGS. 2 and 3, a typical prior stripping and cutting station 1 of an insulated conductor processing machine is illustrated. The prior cutting and stripping station 1 includes a conventional machine frame schematically illustrated at 3. Mounted on the frame 3 for relative transverse reciprocation in the directions of arrow 5 are a front tool holder 7 and an independent rear tool holder 9. Each tool holder 7 and 9 includes a pair of longitudinally spaced apart upstanding shoulders 11 and 13, respectively. The shoulders 11 and 13 are threaded to receive set screws 15 or similar fasteners. Mounted between the respective inside faces 17 of the shoulders are a series of spacers and blades. The front tool holder carries spacers 19 together with known stripping blades 21 and 23 and cutoff blade 25. In applications that call for only one end of an insulated conductor piece 36 to be stripped of insulation 41, only one stripping blade, 21 or 23, is employed.
The rear tool holder 9 carries spacers 27 together with stripping blades 29 and 31 and a cutoff blade 33. The pairs of stripping blades 21, 29 and 23, 31 are located with respect to each other such that as the front and rear tool holders 7 and 9, respectively, reciprocate transversely in the directions of arrow 5, the stripping blades close over and slice the insulation 41 of the insulated conductor 35, which lies perpendicular to the direction of blade motion. Simultaneously, the cutting blades 25 and 33 cooperate to sever the insulated conductor along line 43. Subsequent longitudinal motion of the closed stripping blades relative to the fixed insulated conductor pulls the cut lengths of insulation from the inner conductor 39.
In theory, the cutting edge faces 49 and 51 of the cutoff blades 25 and 33, respectively, coincide to create the cutting line 43. See FIG. 1. Similarly, the cutting edge faces 53 and 55 of the blades 21 and 29, respectively, desirably coincide to form stripping line 47. The cutting edge faces 57 and 59 of the blades 23 and 31, respectively, theoretically coincide to create stripping line 45. To control the relative locations of the cutoff and stripping blades on the independent tool holders 7 and 9, as well as to set the strip lengths A1 and A2, spacers 19 and 27 have traditionally been inserted between the stripping and cutoff blades. The spacers are normally supplied in incremental lengths ranging from approximately 0.03 inches to approximately 0.50 inches.
Given the common strip lengths A1 and A2 required in various industrial applications and the available supply of spacers, different spacers of varying lengths must be stacked together to obtain the desired strip lengths. The stacking of several spacers results in a build-up of the tolerances of the individual spacers. Experience and investigation have shown that the selection of the various individual spacers is done at random, with no regard for the consequential meshing problems inherent in aligning a blade on one tool holder 7 or 9 with the corresponding blade on the other tool holder.
As a result of the stacked spacer tolerance problem, invariably the pairs of cooperating cutting edge faces 49, 51; 53, 55; and 57, 59 on the independent tool holders 7 and 9 do not coincide. As a result, one of two undesirable conditions occurs between a set of blades 21, 29; 25, 33; and 23, 31. The first undesirable condition is that there is interference between the corresponding blades upon closing. The presence of interference is reflected in wear patterns on the cutting edge faces of the blades. The wear patterns may range from faint discoloration to severe gouges. To permit blade closing despite the interference, the blade leading ends are manufactured with bevels 37. Interfering blades deflect each other as they close, with the deflection being governed by the blade thickness. Too much interference may cause the blades to break.
The second undesirable condition that may be caused by tolerance stack-up of the spacers 19 and 27 is the opposite of blade interference. Instead of interference, air gaps may be formed between the cutting edge faces of a cooperating pair of blades. With air gaps between the pairs of stripping blades 21, 29 and 23, 31, the slice made on one side of the insulated conductor insulation 41 by one cutting blade does not meet the slice on the opposite side made by the other blade. Consequently, the insulation is torn when the closed stripping blades are moved longitudinally with respect to the stationary insulated conductor 35 to strip the insulation from the inner conductor 39. The remaining insulation then has a jagged and uneven end surface along strip lines 45 or 47. Extensive experimentation has shown that the insulation tearing force is directly proportional to the air gap between closed blades. Further, the increase in tearing force with air gap is linear. Depending on insulation type, excessive force can cause insulation stretching before breaking and thereby result in a strip length A1 or A2 that is shorter than desired. In addition, the jagged or stretched insulation can slip under the conductor crimp of a terminal fitting applied to the stripped conductor wire 39. Observations of the spacer problems indicate that the air gap problem is more important than the interference problem in causing strip related failures.
Another disadvantage of spacers 19 and 27 of the prior processing stations 1 is that historically their heights and widths have closely coincided with the machine tool holder cavities. In other words, the tops of the spacers have been flush with the tops of the tool holders 7 and 9. That design has required a very cumbersome and aggravating procedure for changing blade set ups, because it is awkward and difficult for the machine operator to remove the spacers from the tool holders with his fingers.
Thus, a need exists for a solution to the problems of insulated conductor strip related failures as well as to the inconvenience of prior blade setup procedures.